The present invention relates to a DC-DC converter.
As a power unit of a device using a battery as an energy source such as a portable telephone and a mobile-related device, a linear regulator is general. In this linear regulator, the loss in the holding area having a small supply (load) current is comparatively small, though a loss depending on the product of the load current and the differential voltage between the supply voltage and the output voltage is generated. An example that this point is taken into account is indicated in xe2x80x9cControl Method for Voltage Drop Chopper Type DC-DC Converterxe2x80x9d disclosed in Japanese Patent Application Laid-Open No.11-341797.
The constitution, operation, and problems of a conventional voltage drop chopper type DC-DC converter will be explained by referring to FIG. 15. In FIG. 15, numeral 1 indicates a DC source, 2 a channel P power MOSFET, 3 a reflux diode, 4 a DC reactor, 5 a smoothing condenser, 6 a load, 21 an output feedback circuit, 22 a PWM (pulse width modulation) control circuit, and 23 a change-over switch.
When the load 6 is a rated load, the change-over switch 23 is kept down on the side of the PWM control circuit 22. By doing this, the output voltage feedback circuit 21 inputs the voltage of the smoothing condenser 5, amplifies the difference from a preset output voltage reference value, and outputs it as an error signal (an analog signal). The PWM control circuit 22 converts the error signal output from the output voltage feedback circuit 21 to a pulse train, turns the channel P power MOSFET2 ON or OFF by the pulse train, thereby executes the PWM control of the voltage.
On the other hand, when the load 6 is reduced to a light load, the PWM control circuit 22 switches the change-over switch 23 to the direction in which the error signal output from the output voltage feedback circuit 21 is directly applied to the channel P power MOSFET2. In this state, the error signal output from the output voltage feedback circuit 21 is immediately applied to the gate electrode of the channel P power MOSFET2. By doing this, the channel P power MOSFET2 operates as an amplifier (a variable resistor) driven by the error signal and operates as a linear regulator for dropping and outputting the voltage input from the DC source 1.
Meanwhile, in correspondence with advanced devices using a battery as an energy source such as a portable telephone and a mobile-related device, improvement of the processing capacity of a CPU (central processing unit) incorporated in these devices is a necessary problem and the CPU is apt to reduce the supply voltage due to increasing of the processing speed. As a result, a power unit mounted in these devices requires voltage drop type DC-DC power conversion having a large difference between the input voltage and the output voltage compared with the conventional one. In these devices using a battery as a power supply, needless to say, the power conversion efficiency of the power unit is an important factor.
However, it cannot be said that the conventional power unit as mentioned above has a sufficient conversion efficiency against the tendency of the CPU of reduction in supply voltage. Firstly, the efficiency xcex7 in the linear regulator operation is almost expressed by the following formula assuming the input voltage as Vin and the output voltage as Vout:
xcex7=Vout/Vinxe2x80x83xe2x80x83(Formula 1)
From Formula 1, xcex7 is proportional to the output voltage Vout under the condition that the input voltage Vin is fixed, so that when the output voltage Vout decreases, the efficiency xcex7 decreases.
On the other hand, with respect to the PWM control, it is well known that as the load is made lighter, the switching loss and driving loss are dominant and the efficiency xcex7 decreases remarkably.
An object of the present invention is to solve a problem that in a DC-DC converter, the efficiency reduces in a light load area or an area having a large difference in output voltage.
The present invention reduces the control loss by the PWM control, PAM switch control, or linear regulator control depending on the load condition or by controlling the output voltage by switching the PWM control, PAM switch control, or linear regulator control and concretely, the present invention is:
a DC-DC converter for converting and outputting the voltage of a DC source to a more lower DC voltage by controlling a semiconductor device characterized in that the peak value of the pulse train to be applied to the control terminal of the semiconductor device is changed, thereby the ON voltage of the semiconductor device is adjusted and the DC voltage to be output is controlled stably, or
a DC-DC converter for converting and outputting the voltage of a DC source to a more lower DC voltage by controlling a semiconductor device characterized in that the pulse width of the pulse train to be applied to the control terminal of the semiconductor device is adjusted and the output voltage is controlled and when the output current is reduced to a predetermined value or less, the peak value of the pulse train is changed in the state that the pulse width is kept at a predetermined value, thereby the ON voltage of the semiconductor device is adjusted and the output voltage is controlled stably, or
a DC-DC converter for converting and outputting the voltage of a DC source to a more lower DC voltage by controlling a semiconductor device characterized in that when the load factor is higher than a predetermined value, the frequency of the pulse train to be applied to the control terminal of the semiconductor device is controlled and when the load factor is lower than the predetermined value, the peak value of the pulse train is changed, thereby the ON voltage of the semiconductor device is adjusted and the output voltage is controlled stably, or
a DC-DC converter for converting and outputting the voltage of a DC source to a more lower DC voltage by controlling a semiconductor device characterized in that the frequency of the pulse train to be applied to the control terminal of the semiconductor device is adjusted and the output voltage is controlled and when the output current is reduced to a predetermined value or less, the frequency is kept at a predetermined value and the peak value of the pulse train is changed, thereby the ON voltage of the semiconductor device is adjusted and the output voltage is controlled stably, or
a DC-DC converter for converting and outputting the voltage of a DC source to a more lower DC voltage by controlling a semiconductor device characterized in that the peak value of the pulse train to be applied to the control terminal of the semiconductor device is changed, thereby the ON voltage of the semiconductor device is adjusted, and when the load factor is lower than a predetermined value, the control for applying the pulse train to the control terminal is changed to the control for continuously increasing or decreasing the voltage to be applied to the control terminal, thereby the output voltage is controlled stably, or
a non-insulated voltage drop type DC-DC converter for converting and outputting the voltage of a DC source to a more lower DC voltage by controlling a semiconductor device characterized in that at a rated load, the pulse width of the pulse train to be applied to the control terminal of the semiconductor device is adjusted to a predetermined value or more and the output voltage is controlled and when the output current is reduced to the first predetermined value or less, the pulse width is adjusted to the predetermined value, and the frequency of the pulse train is limited to a predetermined value or higher, and the output voltage is controlled, and when the output current is reduced less than the second value which is smaller than the first value, the frequency is adjusted to the predetermined value and the peak value of the pulse train is changed, thereby the ON voltage of the semiconductor device is adjusted and the output voltage is controlled, and when output current is reduced less than the third value which is smaller than the second value, the control for applying the pulse train to the control terminal is changed to the control for continuously increasing or decreasing the voltage to be applied to the control terminal, thereby the output voltage is controlled stably, or
a DC-DC converter for converting and outputting the voltage of a DC source to a more lower DC voltage by controlling a semiconductor device characterized in that the DC source is connected to one output terminal of the semiconductor device and the peak value of the pulse voltage to be output to the other output terminal of the semiconductor device is changed, thereby the output voltage is controlled stably.